Synergy lets you easily share a single mouse and keyboard between multiple computers with different operating systems, each with its own display, without special hardware. It's intended for users with multiple computers on their desk since each system uses its own monitor(s).

Redirecting the mouse and keyboard is as simple as moving the mouse off the edge of your screen. Synergy also merges the clipboards of all the systems into one, allowing cut-and-paste between systems. Furthermore, it synchronizes screen savers so they all start and stop together and, if screen locking is enabled, only one screen requires a password to unlock them all. Learn more about how it works.

Synergy is open source and released under the GNU Public License (GPL).

that's a real life saver, just installed it, I'm a happy guy, it cleared up my desk space.
no I just have to figure out how to make the mac command key act as control on Windows as it's little out of reflex to switch it each time